1. Field of the Invention
The present invention relates to an apparatus for measuring the weight of a bulk material conveyed by a conveyor. More specifically, the present invention relates to an improved apparatus for accumulating in an electronic manner the weight of a bulk material continuously conveyed by a conveyor.
2. Description of the Prior Art
A belt conveyor has been widely used for transporting a bulk material, such as a powder like material, grain like material, or the like. In transporting such a material, it is desired to measure the weight of the material placed on the conveyor, while it is conveyed. It is well known that the weight of a bulk material to be conveyed continuously by a conveyor is associated with the product of an instantaneous value of the weight at a given measuring point of the conveyer and the conveying speed of the conveyor. A certain type of an apparatus for measuring the weight of a bulk material placed on and conveyed by a conveyer employing such a principle has been proposed and has been in practical use. Such a conventional measuring apparatus comprises means for generating pulses the frequency of which is associated with the conveying speed of a conveyer belt and a load cell for generating an analog voltage signal associated with the value of a bulk material placed on and conveyed by the conveyer belt at a given measuring point. The analog voltage signal is converted by means of an analog-to-digital (A/D) converter into a bit serial digital signal or pulse signal as a function of the said conveyor speed associated pulse signal. More specifically, the said conveyor speed associated pulse signal is counted by a counter to provide an output at every predetermined number of the conveyer speed associated pulses. An integrator included in the said A/D converter is enabled by the said output from the counter to integrate the analog value whereupon the said stored value is caused to be discharged at a predetermined time constant, the time period of the discharging being representative of the analog value. A pulse representative of the discharging time period is obtained to allow a train of clock pulses obtained from a separate clock source to pass through such that the number of passing clock pulses may be associated with the discharging time period and thus the analog value. The train of the clock pulses thus allowed to pass through is withdrawn by way of the said bit serial digital signal or pulse signal. As the weight of the material increases, the number of bit serial pulse signals obtainable at every said predetermined number of conveyer speed associated pulses increases. Since the said bit serial digital signal is obtained concentratively at intervals of every predetermined number of conveyer speed associated pulses, it is necessary that the frequency of the digital signals and thus the clock pulses from the clock source should be rather high. Accordingly, a counter for cumulatively counting the number of the bit serial digital signal pulses need be of a high speed counter. In general, however, a high speed counter is susceptible to a noise and thus is liable to give rise to an error of measurement. Since the above described conventional apparatus does not hold an instantaneous value of the measured weight at each A/D conversion, such apparatus is not suited for measurement of an instantaneous value of the weight and thus for provision of a quantitative output of an instantaneous weight value.